This invention relates to a novel method for the preparation of homogeneous stabilizer compositions for vinyl halide polymers, the stabilizer compositions so prepared, and to vinyl halide polymers stabilized therewith. More particularly, the invention relates to a process for preparing homogeneous compositions comprising epoxidized glycerides such as vegetable oils, and hydrocarbon-soluble basic alkali and alkaline earth metal salts of alkyl phenols and/or monocarboxylic acids.
Many organic polymers, more particularly halogen containing organic polymers are conveniently and economically processed into useful articles of commerce by methods employing heat to melt or soften the polymer. The use of such heat can be and often is detrimental to the polymer, especially where the polymer is exposed to high (100.degree. C. to 200.degree. C.) processing temperatures for any extended period of time. It is well known that many organic polymers, including halogen containing organic polymers, will undergo color changes and various other physical changes upon exposure to high temperatures over a period of time unless properly protected. The color change is gradual but visually perceptable during short-term exposure to high processing temperatures, but on exposure to high processing temperatures the change in color accelerates and becomes greater in intensity. Color changes occuring during the first several minutes of exposure to high processing temperatures are commonly referred to as early color or early discoloration. Avoidance of such early color or early discoloration is particularly important where white or light colored products are to be produced. It is of course also important to prevent or reduce discoloration and deterioration of the organic polymer during extended exposure to high processing temperatures as may be encountered in some processes or fabricating methods.
A variety of stabilizer systems have been suggested and used to inhibit or prevent this deterioration. These stabilizer systems are for the most part presumed to act in such a manner as to neutralize hydrogen halide that is generated to prevent further dehydrohalogenation which could result because of the presence of free hydrogen halide. Among the stabilizer systems that have been suggested and used in the prior art are oil-soluble salts of such metals as barium, cadmium, zinc, zirconium, tin, calcium. Generally, the above metal salt stabilizers are used in combination with one or more organic phosphites.
In many applications, the stabilizer systems incorporated into vinyl halide polymers will contain an auxiliary stabilizer which is an epoxidized vegetable oil, an epoxidized fatty acid, or an ester of an epoxidized fatty acid such as epoxidized soybean oil, epoxidized tall oil, and butyl epoxy stearate.
In the commercial use of stabilizer systems for vinyl halide polymers, has become common practice to prepare mixtures of the various stabilizers which facilitate the handling and storage of the stabilizers. For example, useful stabilizer systems comprising blends of oil-soluble salts of polyvalent metals, organic phosphites, and auxiliary stabilizers such as epoxidized soybean oils are often prepared for use as needed.
A variety of oil-soluble salts of monovalent and polyvalent metals have been utilized as stabilizers for vinyl halide polymers. The metals include the alkali metals, zinc, calcium, tin, barium, aluminum, strontium, zirconium and magnesium. The metal salts may be neutral salts although basic or "overbased" metal salts are preferred since these contain larger amounts of the metal. In some applications, mixtures of neutral and metal basic salts are utilized such as mixtures of neutral cadmium carboxylates with overbased barium phenates, carboxylates and/or sulfonates.
U.S. Pat. No. 4,159,973 describes stabilizer systems for vinyl halide resin compositions which comprise mixtures of (a) specified overbased barium salt complexes that are compatible with epoxidized vegetable oil, (b) a polyvalent metal salt component, (c) at least one organic phosphite, and (d) an aromatic or aliphatic hydrocarbon solvent. Examples of the polyvalent metal salts include cadmium, zinc, zirconium, tin and calcium salts of aromatic as well as aliphatic carboxylic acids. The organic phosphites may be secondary or tertiary aryl, alkyl or alkaryl phosphites. It is reported that vinyl halide resin compositions containing such stabilizer systems are characterized by excellent heat and light stability, color and clarity.
An anti-yellowing additive for stabilizing vinyl chloride polymers is described in U.S. Pat. No. 4,252,698. The additive comprises the mixture of at least one overbased sulfonate or phenolate compound of lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, titanium, aluminum, zirconium or tin, and a 1,3-di-ketone compound having about 5 to about 30 carbon atoms or a metal salt thereof wherein the metal may be any one of the metals described above for the overbased sulfonate or phenolate compound.
U.S. Pat. No. 3,194,823 describes barium- and cadmium-containing organic complexes useful in stabilizing halogen-bearing polymeric compositions. In general, the complexes are prepared from a mixture comprising (a) an alcohol, (b) an aliphatic monocarboxylic acid compound, and (c) a mixture of barium and cadmium bases optionally in the presence of a phenol. Such cadmium- and barium-containing basic complexes can be utilized in vinyl halide polymers in combination with other stabilizing agents such as epoxidized soybean oil and organic phosphites.
The polyvalent metal components of the stabilizers which have been utilized for vinyl halide polymers usually contain a barium compound which may be a salt of a monocarboxylic acid such as octanoic acid, neodecanoic acid, or naphthenic acid; a salt of an alkyl phenol such as octyl phenol, nonyl phenol, etc.; or an overbased barium salt complex. The use of overbased barium salt complexes has increased in recent years because the overbased salts contain high amounts of barium such as, for example, 21 to 35% barium or higher.
Overbased barium salt complexes are well known, and various procedures for preparing such overbased barium salt complexes from carboxylic acids, sulfonic acids and alkyl phenols using an acidic gas such as carbon dioxide or sulfur dioxide to reduce the basicity are disclosed in, for example, the following U.S. Pat. Nos.: 2,616,904; 2,760,970; 2,767,164; 2,798,852; 2,802,816; 3,027,325; 3,031,284; 3,342,733; 3,533,975; 3,773,664; and 3,779,922.
While many overbased barium salts such as the overbased barium alkyl phenate complexes described in some of the above patents are effective stabilizers for vinyl halide polymers, they often are incompatible with epoxidized soybean oil and other epoxidized vegetable oils. When the overbased barium compounds are combined, for example, with conventional oil-soluble cadmium and/or zinc carboxylic acid salts and organic phosphites, and the resulting stabilizer system is blended with an epoxidized vegetable oil, the resulting blend generally becomes cloudy as the incompatible components precipitate. Because such blends are not homogeneous, they present handling and storage problems.
U.S. Pat. No. 4,159,973 describes overbased barium salt complexes that are compatible with epoxidized vegetable oils. The barium salts are obtained by forming a reaction mixture that consists essentially of a basic barium compound, an alkyl phenol and an inert organic diluent wherein the mixture contains at least 0.75 mole of alkyl phenol per mole of the barium compound, and the reaction mixture is maintained at a temperature of at least 180.degree. C. while treating it with an acidic gas such as carbon dioxide until the product is substantially neutral. If less than 0.75 mole of alkyl phenol is included in the mixture, and the mixture is treated with carbon dioxide at a temperature below 180.degree. C., the barium compound obtained is reported to be incompatible with epoxidized vegetable oils.
U.S. Pat. No. 4,401,779 issued Aug. 30, 1983 to Bae et al describes homogeneous liquid stabilizer systems which impart heat and light stability to polyvinyl chloride resins. The systems contain as the essential and only stabilizers, a liquid barium carbonate-barium alkyl phenate and a cadmium salt of a branch chain aliphatic carboxylic acid having from about 8 to about 10 carbon atoms, or mixtures thereof in an amount of at least which 85% with up to about 15% of one or more cadmium salts of aromatic carboxylic acids having from about 7 to about 11 carbon atoms and saturated and unsaturated straight chain aliphatic carboxylic acids having from about 12 to about 22 carbon atoms. The barium and cadmium salts are present in amounts sufficient to form a homogeneous liquid.